Acquisitions Redeemable Noncontrolling Interests (Details) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017
Redeemable Noncontrolling Interests
Balance at beginning of period	$ 252.1	$ 252.8
Change in related noncontrolling interests balance	(15.5)	(9.5)
Changes in redemption value of redeemable noncontrolling interests:
Additions	0.0	3.4
Redemptions	(33.7)	(18.5)
Redemption value adjustments	(43.2)	9.8
Balance at end of period	$ 159.7	$ 238.0

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Change in noncontrolling interest balance related to redeemable noncontrolling interests

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Redeemable noncontrolling interests period increase

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Adjustments to the Redemption Value of Redeemable Noncontrolling Interests

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Decrease in noncontrolling interest (for example, but not limited to, redeeming or purchasing the interests of noncontrolling shareholders, issuance of shares (interests) by the non-wholly owned subsidiary to the parent entity for other than cash, and a buyback of shares (interest) by the non-wholly owned subsidiary from the noncontrolling interests).

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The aggregate fair value as of the reporting date of all noncontrolling interests which are redeemable by the (parent) entity (1) at a fixed or determinable price on a fixed or determinable date, (2) at the option of the holder of the noncontrolling interest, or (3) upon occurrence of an event that is not solely within the control of the (parent) entity. This item includes noncontrolling interest holder's ownership (or holders' ownership) regardless of the type of equity interest (common, preferred, other) including all potential organizational (legal) forms of the investee entity.

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